2006 Honda Accord threw P0139 code

check engine light throwing P0139 code; replaced o2 sensor downstream with factory OEM sensor; light reset and code stayed gone for several months now it is back? need a plan before attempting more costly computer replace??

The P0139 code can mean a leaking fuel injector is allowing fuel to leak into the engine when you remove your foot from the throttle. It expects the O2 sensor to read a low value but it isn’t. It may also be caused by excess oil in the exhaust stream but you should know that from the look of the O2 sensor your replaced and oil consumption. Try a bottle of injector cleaner in the gas tank as a quick-and-dirty fix. If that doesn’t work you need to find if there is a leaking injector.

@Mustangman is right about the causes.

You replaced the O2 censor for no reason.
The Code P0139 was telling you that there was a problem with that O2 sensor not receiving the correct levels within the computer’s parameters…Not that you should replace the O2 sensor.

Good thing you came here before you replaced the Computer!!!


Some ideas

  • Could be an intermittent electrical connection at the sensor or the ECM. Visually check the wiring and connectors at the sensor and ECM.
  • Could have an air/fuel ratio problem, caused by faulty MAF, intake air leak, exhaust leak, or faulty injector(s). If you are aware of any air or exhaust leaks, fix those before assuming the cause is something else.
  • Have the shop measure the fuel trims to assess further evidence of an air/fuel mixture problem.
  • Any repairs done on the engine that used silicone sealant or caulk? If the non-automotive version of that product is used, sometimes it can damage the O2 sensor.
  • Any oil or coolant dripping on the external part of the O2 sensor? The sensor has microscopic passages in it to allow air to get inside to the working tip. It need the air passage to be free to work correctly. If those passages are clogged from something dripping on it, it won’t work correctly.
  • Ask the shop if they have the test equipment needed to measure the O2 sensor output signal. Assuming they know how to interpret it, that can provide a clue to what’s wrong.

There is a PCM software update to correct an erroneous P0139 fault on the 4 cylinder Accord, check with your Honda dealer.

There’s a TSB about re-flashing of the PCM to address this code error.